1. Field of the Invention
The present invention relates to a construction machine having a multi-articulated front device, and more particularly to a front control system for a construction machine, e.g., a hydraulic excavator having a front device comprising a plurality of front members such as an arm, a boom and a bucket, which system is adapted for front control, e.g., area limiting excavation control to limit an area where the front device is allowed to move for excavation. The present invention also relates to an oil temperature indicator for use in the front control system.
2. Description of the Related Art
There is known a hydraulic excavator as typical one of construction machines. In a hydraulic excavator, front members, such as a boom and an arm, making up a front device are operated by an operator manipulating respective manual control levers. However, because the front members are coupled to each other through articulations for relative rotation, it is very difficult to carry out excavation work within a predetermined area or in a predetermined plane by operating the front members. Also, when excavation work is performed in urban districts and so forth, due care must be paid to keep the front device from interfering with surrounding objects, e.g., electric wires and walls.
In view of the above-mentioned state of art, various proposals for facilitating excavation work or preventing interference between the front device and surrounding objects have been made.
For example, according to JP, A, 4-136324, a slowdown area is set in a position before reaching an entrance forbidden area, and a front device is slowed down by reducing an operation signal input from a control lever when a part, e.g., a bucket, of the front device enters the slowdown area, and is stopped when the bucket reaches the boundary of the entrance forbidden area.
Also, according to WO 95/30059, an area to be excavated is set beforehand, and a part, e.g., a bucket, of a front device is controlled to slow down its movement only in the direction toward the excavation area when the bucket comes close to the boundary of the excavation area, and to be able to move along the boundary of the excavation area without going out of the excavation area when the bucket reaches the boundary of the excavation area.
Meanwhile, in machines wherein working members are driven with hydraulic pressure, such as hydraulic excavators, a hydraulic pump is rotated by a prime mover to deliver a hydraulic fluid (oil) therefrom for driving a hydraulic actuator. As with ordinary motor vehicles, such a hydraulic machine requires warm-up operation of the prime mover at the start-up. To inform the operator of that the machine is now under the warm-up operation, therefore, an actual machine includes a thermometer for detecting a temperature of cooling water for the prime mover and a warmup lamp. The warm-up lamp is lit up when the water temperature is not higher than a predetermined value, and is turned out when it exceeds the predetermined value.